Vehicles equipped with internal combustion engines and automatic transmissions are calibrated to shift transmission gears during ongoing operation based upon predetermined criteria. Shifting between gear ratios in an automatic transmission is driven by operator demand for power, typically as an input to an accelerator pedal and an engine throttle device. In one maneuver, referred to as a tip-out-up-shift, a typical transmission executes an up-shift event, i.e. shifting from a lower gear to a higher gear, when the operator releases or ‘tips out’ of the accelerator pedal, leading to a closing of the throttle device.
In a hybrid vehicle or a conventional powertrain vehicle which has been calibrated for optimal fuel economy, the control system often cuts fuel when the operator tips out of the accelerator pedal, especially when the accelerator pedal returns to a neutral position. The control system attempts to cut fuel delivery as quickly as possible to achieve a maximum fuel economy benefit. On hybrid systems employing regenerative braking, there is a further desire to ramp in such action as quickly and deeply as possible, while still meeting vehicle driveability requirements.
In a vehicle equipped with a step-automatic transmission, when the operator tips out the accelerator pedal from point A to B (shown in FIG. 1) the exemplary transmission performs a tip-out up-shift as the pedal position transitions across a 3-4 up-shift line, shown as AD. Thus, for a deceleration from operating point A having a vehicle speed of about 105 kilometers per hour (‘kph’) and an accelerator pedal position starting at about 50% and going to near 0%, the following undesirable actions can occur. The action of tipping out of the accelerator pedal as described causes the transmission to begin to execute a shift-up, and set a shift-in-progress flag. Any scheduled cut in fueling is suspended while the shift-in-progress flag is set, thus delaying start of any deceleration-induced fuel cut. Activation and slewing of regenerative braking is reduced during the shift, thus reducing ability to recapture energy. There is also a tip-out up-shift driveline disturbance. After the shift is complete, fuel cutoff (FCO) is entered. Though the individual driveline disturbances of the up-shift and fuel cutoff entries may be small, the successive events can have a noticeable compounding effect. When the operator brakes the vehicle, a 4-3 downshift (i.e., from fourth gear to third gear) occurs, shown as line BC, resulting in another driveline disturbance. During the 4-3 downshift, regenerative braking is reduced to minimize driveline disturbances. Once the transmission is in third gear, regenerative braking is slewed back in to continue FCO. Furthermore, inhibiting the 3-4 tip-out up-shift results in greater engine speed, resulting in higher regenerative braking power and ability to recapture vehicle kinetic energy.
It is desirable to have a vehicle control system which is able to take more complete advantage of benefits derived from cutting off of fuel and regenerative braking during vehicle deceleration events.
Therefore, a method and system are offered which address the above-stated concerns and permits the vehicle to take more complete advantage of benefits achievable during vehicle deceleration.